Yoshiyuki Soeda

Abstract Prior to the formation of amyloid fibrils, the pathological hallmark in tau-related neurodegenerative disease, tau monomers aggregate into a diverse range of oligomers. Granular tau oligomers, consisting of approximately 40 tau protein molecules, are present in the prefrontal cortex of patients at Braak stages I-II, preclinical stages of Alzheimer’s disease (AD). Antibodies to granular tau oligomers as antigens have not been reported. Therefore, we generated new rat monoclonal antibodies by immunization with granular tau oligomers. Three antibodies from different hybridoma clones showed stronger immunoreactivity to granular tau oligomers and tau fibrils compared with monomeric tau. Of the three antibodies, 2D6-2C6 showed 3000-fold greater immunoreactivity in P301L-tau transgenic (rTg4510) mice than in non-transgenic mice, while MC1 antibody, which detects pathological conformations of tau, showed a 5.5-fold increase. These results suggest that 2D6-2C6 recognizes aggregates more specifically than MC1. In AD subjects, 2D6-2C6 recognized neurofibrillary tangles and pretangles, and co-localized within AT8-positive cells containing phosphorylated tau aggregates. The epitope of 2D6-2C6 is the 423–430 amino acid (AA) sequence of C-terminal regions. Taken together, a novel monoclonal antibody, 2D6-2C6, generated by immunization with granular tau oligomers binds to tau aggregates at the 423–430 AA sequence.

Tauopathy is a group of diseases characterized by fibrillary tau aggregate formation in neurons and glial cells of the brain. Tau aggregation originates in the brainstem and entorhinal cortex and then spreads throughout the brain in Alzheimer’s disease (AD), which is the most prevalent form of tauopathy. Understanding the mechanism by which locally formed tau pathology propagates throughout the brain is crucial for comprehending AD pathogenesis. Therefore, a novel model of tau pathology that artificially induces tau aggregation in targeted cells at specific times is essential. This study reports a novel optogenetic module, OptoTau, human tau with the P301L mutation fused with a photosensitive protein CRY2Olig, which induced various forms of tau according to the temporal pattern of blue light illumination pattern. Continuous blue light illumination for 12 h to Neuro2a cells stably expressing OptoTau (OptoTauKI cells) formed clusters along microtubules, many of which eventually accumulated in aggresomes. Conversely, stable tau aggregates were formed when alternating light exposure and darkness in 30-min cycles for 8 sets per day were repeated over 8 days. Stable tau aggregates were induced more rapidly by repeating cycles of 5-min illumination followed by 25 min of darkness over 24 h. These results indicate that OptoTau induced various tau aggregation stages based on the temporal pattern of blue light exposure. Thus, this technique demonstrates potential as a novel approach to developing specific tau aggregation in targeted cells at desired time points. Significance This study developed a technique to manipulate tau aggregation in a blue light-dependent manner using cells that stably express OptoTau, which is an optogenetic tool based on the CRY2Olig module. Tau accumulation in aggresomes or insoluble tau aggregation were specifically induced in response to blue light illumination conditions. These results are crucial as they provide a new technological basis for developing a singular point of tau aggregation in specific targeted cells at a specific time.